With the constant development of the semiconductor technology, more and more functions are integrated onto a small sized wafer substrate, and the wires laid on the wafer substrate are denser and denser. The device with 65 nm wide wires has been successfully developed at present, and the device with 45 nm wide wires will be produced in large scale finally. With the gradual popularization and application of the fine pitch or ultra fine pitch lead bonding technology, the space between a wire and a conductor becomes smaller and smaller, achieving 60-40 um, and even as small as 35-30 um within a few years in the future. As a result, a chip having the same size as before has more and more powerful functions nowadays.
The wire welded on a wafer usually has the diameter of 25.4 um/20 um or even thinner e.g. 18 um. And the diameter of a corresponding welding gold ball is 32 um-50 um. Those connecting wires and gold ball welding points must be firmly and reliably welded on a weld pad on a wafer substrate. The welded object to be tested is so small that a great part of the test force values are concentrated within the range from 2-3 g to 100 g. Therefore, how the test device ideally and conveniently applies a traction force test action to obtain a mechanical test result appropriating to the firmness of the tested object to the most extent, has become an issue worth to study in this field.
A known test device uses a thin hooked needle to hook the welding lead to be tested in the IC via a force sensor, and does pull and push actions to measure the firmness of the welding lead or the strength of the lead itself in a destructive or non-destructive manner. The basic principle is very simple. However in fact, the requirements for the test in the practical process are far from as simple as mentioned in the above principle.
The force sensor can deform whenever under stress, thus the magnitude of the test force can be identified according to the deformation of an elastic body. A former test instrument uses a force sensor having a cantilever beam structure as shown in FIG. 1; a test tool 3 with a certain length and having a very thin hook 2 arranged at the tip is installed at the front end of the cantilever beam 1; when a test force is applied onto the test tool 3, the force sensor of the cantilever beam structure bends and deforms under the effect of the test force F. Different levels of test forces cause different degrees of bending deformation. The rigid test tool 3 installed at the front end of the sensor forms a rotation angle A (as shown in FIG. 2) in the direction of the test force F, which is unexpected for the test itself, thus influencing the truthfulness of the test result. The quantitative association between the degrees of bending deformation, the rotation angle A and the test force will not be discussed herein. As a matter of fact, it is extraordinarily complex to accurately quantify the above association. However, it is obvious that the test tool may cause awful things due to the rotation angle A generated along with the bending deformation of the force sensor of the cantilever beam: during the test of a product with dense welding leads in the IC, the hook 2 at the front end of the test tool 3 having the rotation angle A may cause damage to the welding lead in an un-tested IC beside.
Another solution for testing the traction of the welding lead in the IC by employing a force sensor with double cantilever beams having the same length is as shown in FIG. 3. Under the effect of the test force F, the first cantilever beam 11 and the second cantilever beam 12 with the same length have almost the same bending deformation, so the test tool 3 and the hook 2 at the front end thereof can still maintain the vertical attitude, thus avoiding the occurrence of the rotation angle A as mentioned above. However, it can also be easily observed that the test tool 3 and the hook 2 at the front end thereof have a displacement X. That is to say, during the test of a product with dense welding leads in the IC, the hook 2 at the front end of the test tool may still cause damage to the welding lead in an un-tested IC beside. The dashed line part in the figure is the state of the force sensor when the test force F is not applied.
An U.S. patent: U.S. Pat. No. 6,301,971 provides another solution: employing a force sensor with double cantilever beams having unequal lengths. As shown in FIG. 4, under the effect of the test force F, the unequal first cantilever beam 11 and second cantilever beam 12 have different bending deformations due to the different lengths. The specific and accurate relationship between the bending deformation and the applied test force is extraordinarily complex. As for the force sensor with double cantilever beams having unequal lengths, when the test force is applied, the test tool 3 and the hook 2 at the front end thereof will rotate in a pre-designed inclination direction, with the purpose of coinciding the axial direction of the test tool 3 and the hook 2 with the direction of the test force F. However, the prerequisite of the force sensor with double cantilever beams is supposing that the direction of the test force F is inclined. In practice, the directions of the test forces are various, for example, the direction of the hypothetical test force F and the gravity direction of a weight hung for calibrating the sensor; the direction of the test force is difficult to be ensured to coincide with the axial line of the test tool. However, due to the specially designed deflection angle of the test tool when under stress, the offset X at the front end of the test tool has a decreasing trend, thus better reducing the possibility of causing damage to the welding lead in the un-tested IC beside compared with the above solutions. However, the analysis from the principle shows that offset X will still occur at the front end of the test tool 3.